Elastomeric compositions are used in a wide variety of applications, including hoses, belts, footwear components, vibration isolation devices, tires, and tire components such as treads, innerliners, and sidewalls. The selection of ingredients for the commercial formulation of an elastomeric composition depends upon the balance of properties desired, the application, and the application's end use.
For example, in the tire industry the balance between processing properties of the green (uncured) composition in the tire plant and in-service performance of the cured rubber tire composite is of particular importance. The ability to improve the endurance of tires used in a wide variety of conditions, such as is required for agricultural tires, aircraft tires, earthmover tires, heavy-duty truck tires, mining tires, motorcycle tires, medium truck tires, and passenger car tires, while maintaining ease of processability of the uncured elastomeric composition is also of significant importance. Additionally, the goals of improving air impermeability properties, flex fatigue properties, and the adhesion of the elastomeric composition to adjoining tire components without affecting the processability of the uncured elastomeric composition or while maintaining or improving the physical property performance of the cured elastomeric composition still remain.
Conventionally, various processing oils, such as naphthenic, paraffinic, and aromatic oils, have been added to many tire components to aid compound processing. Naphthenic oil has been preferred for tire innerliner compounds due to its processing effectiveness and beneficial secondary properties, e.g. compatibility with isobutylene based elastomers. However, while these conventional processing oils improve processability, this benefit may have an undesirable impact on various other properties, including air impermeability.
Generally, the raw ingredients and materials used in tire compounding impact all tire performance variables, thus, any alternative to conventional processing oils must be compatible with the rubbers, not interfere with the vulcanization rate, be easily dispersed in all tire compounds, be cost effective, and not adversely impact tire performance. This is of particular concern for tire innerliners and tire innertubes where performance properties must be maintained within specified tolerance levels. For example, small increases in a tire innerliner compound's 300% modulus can lead to reduction in fatigue resistance and cracks with consequential loss in tire durability. Furthermore, for an elastomeric composition that acts as an air barrier it is of particular importance that any benefits in compound processability are not to the detriment of the composition's air retention capabilities.
Tubeless tires require elastomeric compositions having high air retention. Halobutyl rubber has been used in tire innerliner compounds to enable improvements in air retention performances, improvements in liner-to-tire casing adhesion, and improvements in tire durability. Additionally, clays have been added to elastomeric compositions to form “nanocomposites” in order to alter the composition's properties and improve air barrier properties. For example, nanocomposites have been formed by adding clay to brominated copolymers of isobutylene and p-methylstyrene. Processing aids such as naphthenic, paraffinic, and aliphatic resins have been used to improve the processability of elastomeric compounds containing nanocomposites. However, these processing aids often increase the elastomeric compositions permeability.
As many tires are compounded and engineered for particular performance characteristics, it is desirable that any replacement for traditional process oils maintains tire performance characteristics, such as rolling resistance, traction, and wear performance. Improvement in air retention qualities can allow improved maintenance of tire rolling resistance performance through the service life of the tire, improved durability, and lower tire operating temperatures, thus there is still a need for a replacement for traditional process oils in tire and tire innerliner compounds which allow for beneficial compound processability and improved tire innerliner impermeability.